This invention relates to structure and method for mounting and interconnecting electronic circuit modules with a low profile.
In present day electronics it is often necessary or desirable to fixedly mount electronic circuit modules on support and interconnect surfaces, such as printed circuit boards, etc. However, in many applications the overall thickness of the mounted modules is a critical parameter that must be kept low.
One prominent method and apparatus for achieving this mounting of modules on a printed circuit board is referred to as a ball grid array (BGA). BGAs include an array of solder balls all having the same relatively large diameter. BGAs are known to provide reliable interconnect for devices with large input/output (I/O) numbers. However, the height ranges from 15 to 35 mils, which has the disadvantage of making the overall height of the device too big.
The use of metal pads for I/O soldering can reduce the interconnect thickness to less than 5 mils, which significantly reduces the overall height of the device when mounted on a printed circuit board. The draw back for metal pads is that the reliability of I/Os is not as good. Due to the low solder height, there is not sufficient solder to relieve the stress generated by thermal mismatch between the module and the printed circuit board.
Accordingly it is highly desirable to provide structure and a method for mounting modules on a supporting and interconnect surface and for achieving a low profile final structure.